There is currently no therapy for ALS and it is universally fatal. The research in this proposal will identify compounds that can inhibit TDP-43 aggregation using inclusion formation as a primary readout. Protein aggregation has been implicated as a primary driving force in multiple neurodegenerative illnesses. TDP-43 is one of the most promising targets for pharmacotherapy of ALS because it is one of the major proteins that accumulate as inclusions in Amyotrophic Lateral Sclerosis (ALS), it shows a strong tendency to aggregate, mutations in TDP-43 cause familial ALS and we observe that mutations increase the tendency of TDP-43 to inclusions composed of aggregated protein. We performed a chemical screen to identify small molecules that inhibit TDP-43 aggregation using the high-throughput resources of the Laboratory of Drug Discovery in Neurodegeneration (LDDN) at Brigham and Women's Hospital. The work in this proposal describes the secondary screens and medicinal chemistry to test for and optimize inclusion inhibition and neuroprotection. The optimization studies used in the proposal will primarily use primary cultures of cortical and motor neurons expressing human TDP-43 (WT and A315T). Some studies will also use neuronal PC12 cells that inducibly express WT TDP-43. In each case, the develop cellular cytoplasmic TDP-43 inclusions. We will also analyze the efficacy of the lead compounds to prevent motor deficits in vivo, using C. elegans expressing TDP-43. Our screen of 75,000 novel compounds and 1600 FDA approved and bioactive compounds identified 22 lead compounds on 10 different chemical scaffolds that inhibit inclusion formation. The work in this proposal will identify those chemicals that also provide neuroprotection in models of TDP-43 neurotoxicity. The work will be done through an iterative process of biological testing in the laboratory of Dr. Wolozin, at Boston University School of Medicine, and chemical optimization via medicinal chemistry, performed at the LDDN. Aim 1 will validate the lead compounds from high-throughput fluorescence inclusion assay. We will take our 22 lead compounds from the screening campaign, and test the ability of each compound to inhibit degeneration and inclusion formation in neuronal models of TDP-43 mediated toxicity. We will examine primary cultures of cortical and motor neurons. We will also examine lines of C. elegans expressing WT or A343T TDP-43, to investigate behavior and inclusion formation. Aim 2 will focus on chemical optimization. We will use medicinal chemistry to optimize the pharmacological properties of the two best lead compounds. We will use an iterative process, in which the lead compounds are chemically modified, tested for inclusion dispersion.